Organic TFTs are known. See, for instance, U.S. Pat. No. 5,347,144. However, until recently, attainable device parameters (e.g., on/of F ratio) were insufficient for most contemplated applications (e.g., as pixel switches in active matrix liquid crystal displays). A. R. Brown (Science, Vol. 270, p. 972, November 1995) disclose logic gates made from polymer transistors.
Recently it has been demonstrated that organic TFTs (more specifically, organic TF field effect transistors or TF-FETs) can be produced to have on/off current ratios &gt;10.sup.6 and switching speeds of about 10 .mu.s. See A. Dodabalapur et al., Science, Vol. 268, p. 270 (1995), and H. E. Katz et al., Proceeding of the PMSE Division of the American Chemical Society, Vol. 72, p. 467 (1995). See also U.S. patent applications Ser. Nos. 08/353,024, and 08/353,032, both filed Dec. 9, 1994 by A. Dodabalapur et al. and co-assigned with this. The relevant disclosures of the cited publications and patent applications are incorporated herein by reference.
More recently still it was discovered that organic TF FETs can be designed such that a given device can function as a n-channel or p-channel device, depending on biasing conditions. See U.S. patent application Ser. No. 08/446,142, filed May 15, 1995 by A. Dodabalapur et al., co-assigned with this and incorporated herein by reference. See also A. Dodabalapur et al., Science, Vol. 269, p. 1560 (September 1995), also incorporated by reference.
As those skilled in the art will recognize, the organic TF FETs of the '142 patent application can be combined to yield complementary circuits, with the attendant advantages of reduced power consumption and simplicity of circuit design.
The devices of the '142 patent comprise an organic p-channel material (exemplarily .alpha.-hexathienylene or .alpha.-6T) and an organic n-channel material (exemplarily C.sub.60). Whereas .alpha.-6T can be a relatively stable material that is more easily deposited in p-type form than many inorganic semiconductors, C.sub.60 and other organic materials that have been made to work as n-channel material typically undergo degradation when used in air. Thus such devices typically require unconventional manufacturing techniques and/or careful packaging in order to attain reasonable lifetimes. Such manufacturing and packaging would at best be expensive (and thus incompatible with many of the low cost applications envisaged for complementary organic TF FETs). The required hermetic packaging may even be incompatible with such contemplated applications as smart cards and RF identification tags, which frequently demand at least a modest degree of mechanical flexibility of the circuitry.
At least until the above referred-to technological difficulties with organic n-channel TF FETs are overcome, it would be of interest to have available a technology for making complementary circuits that is capable of taking advantage of the excellent characteristics of known p-channel organic TF FETs and of n-channel inorganic TF FETs, e.g., amorphous Si TF FETs, without being subject to the problems currently typically associated with organic n-channel TF FETs and inorganic p-channel TF FETs. This application discloses such a technology.